Conformation-specific anti-pathological tau antibody raised against AD brain-derived seed-competent tau reduces tau pathology in transgenic mice

Abstract

Accumulation of intracellular hyperphosphorylated tau protein into aggregates called neurofibrillary tangles is a hallmark of Alzheimer’s disease (AD) and other neurodegenerative diseases. In AD, tau pathology spreads trans-synaptically in a defined pattern, correlating with cognitive decline. We hypothesized that antibodies targeting the tau species responsible for propagation could slow disease progression. However, the identity of these pathogenic tau species remains unclear. We isolated tau species from AD brain tissue using sucrose gradient fractionation and size-exclusion chromatography (SEC) and developed Single Molecule Array (SIMOA) assays to quantify phosphorylated and aggregated tau in each fraction. To evaluate tau species that are competent seeds for initiating tau aggregation, all sucrose fractions were assessed in human embryonic kidney (HEK) biosensor and primary neuronal seeding assays and evaluated in rTg4510 seeding mouse model. Based on their seeding activity, a panel of antibodies was raised against tau species from the 30–50% fractions and characterized in vitro and in vivo assays. Seeding activity was induced in HEK-biosensor cells and primary neurons with 20–50% AD sucrose fractions, but not by non-AD control fractions. No seeding activity was observed with 0% AD fractions. Furthermore, size exclusive chromatography revealed that seeding activity was induced mainly by tau in high-molecular-weight fractions. A mouse immunization campaign with 30–50% AD sucrose fractions containing seeding competent tau species resulted in a novel anti-pathological tau antibody 008 (APTA-008) that selectively recognizes a pathology-specific conformation of tau. In the rTg4510 in vivo tau seeding model, APTA-008 dosed at 10 mg/kg, significantly reduced tau pathology induced by hippocampal injection of AD brain lysate. Our findings reveal that only a low abundant and rare subset of tau species is involved in seeding activity and that this species can be used to raise a conformation- and pathology-specific-antibody against tau. The discovery of APTA-008 offers a promising therapeutic approach for AD and related tauopathies.